The present invention relates to an atmospheric pressure ionization mass spectrometer with an ionization function which utilizes molecular reaction. More particularly, the present invention pertains to an atmospheric pressure ionization mass spectrometer provided with an interface used for on-line coupling of the mass spectrometer to a liquid chromatograph.
It is known to employ an atmospheric pressure ionization mass spectrometer which is coupled on-line to a liquid chromatograph (hereinafter referred to as an "LC") to achieve improvement of analysis performance. An on-line coupled liquid chromatograph/mass spectrometer (hereinafter referred to as an "LC/API mass spectrometer"), which utilizes atmospheric pressure ionization (hereinafter referred to as an "API"), has advantages that cannot be obtained by a conventional on-line coupled gas chromatograph/mass spectrometer (hereinafter referred as an "GC/EI mass spectrometer"), which utilizes electron impact ionization. For example, since the LC/AIP mass spectrometer employs the ionization means which imparts less impact, decomposition of a sample to be ionized is less, thus facilitating observation of molecular ions.
Techniques of on-line coupling of an LC to a mass spectrometer are disclosed in, for example, Japanese Patent Examined Publication No. 58-43692 filed by this assignee and in ANALYTICAL CHEMISTRY, Vol. 58, No. 14 (December 1986), pp, 1451A-1461A.
On-line coupling of the LC to the mass spectrometer requires processing of the liquid output from the LC in a form suitable for spectrometric analysis by the mass spectrometer. Some processing techniques are introduced in the aforementioned text ANALYTICAL CHEMISTRY. The typical interface is an atomization unit for atomizing the sample and the mobile phase which flow out of the LC. The sample and the mobile phase which flow out of the LC are introduced into this atomization unit where they are heated and, thereby, the sample is reduced to molecular particles. In the mass spectrometer coupled on-line to the LC, the sample is first ionized by corona discharge in an ionization chamber, and mass spectrometric analysis is then conducted on the ions.
The conventional atomization units, which are described in, for example, ANALYTICAL CHEMISTRY, Vol. 57, No. 12 (Oct./1985), pp. 2374-2375, employ a thin tube having an inner diameter of 0.1 mm as a sample introducing pipe. This sample introducing pipe is formed integrally with a heater block which is heated to atomize the sample and the mobile phase. In this configuration, however, the temperature of the heater block and the flow rate of the sample and the mobile phase delicately affect atomization thereof, and it is thus very difficult to set the temperature of the heater block adequately, which is required to obtain stable fine particles.
In the LC/API mass spectrometer, atomization of the sample and the mobile phase to stable and minute particles is essential for achieving mass spectrometric analysis at a high sensitivity.